三种方式中最好的一种不是Poll方式，也不是回调方式，而是Wait方式。该方式提供的灵活性最大、效率最高，但有点复杂。使用这种方式，可以编写代码，启动多个异步进程，等待全部或部分进程的完成。这种方式允许只等待互相依赖的进程，然后继续执行不互相依赖的进程。按照其设计，这种方式需要仔细考虑异步进程。必须认真选择出以并行方式运行的异步进程，最重要的是，确定不同的进程如何相互依赖。这种方式的复杂性在于，需要理解其中的细节，并设计出相应的代码。最终结果一般是，非常简洁的代码设计能最大限度地利用同步和异步处理模型。
代码
<body>
<form id="form1" runat="server">
<div>
<asp:GridView ID="gvOrders" runat="server" AutoGenerateColumns="false">
<Columns>
<asp:BoundField HeaderText="Comany Name" DataField="CompanyName" />
<asp:BoundField HeaderText="Contact Name" DataField="ContactName" />
<asp:BoundField HeaderText="Contact Title" DataField="ContactTitle" />
<asp:BoundField HeaderText="Order Date" DataField="OrderDate" DataFormatString="{0:d}" />
</Columns>
</asp:GridView>
</div>
<br />
<div>
<asp:GridView ID="gvCustomers" runat="server">
</asp:GridView>
</div>
</form>
</body>
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
namespace AdoAsyncDB
{
/// <summary>
/// 使用Wait方式
/// </summary>
public partial class WaitMethod : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
GetWaitAnyData();
}
/// <summary>
/// 使用Wait方式
/// 等待句柄关联到异步进程上。使此这种方式，可以启动需要的所有异步进程，等待全部或部分进程的完成，以便对它们执行相应的处理。
/// 使用这种方式，可以编写代码，启动多个异步进程，等待全部或部分进程的完成。这个方式允许只等待互相依赖的进程，然后继续执行不互相依赖的进程。
/// </summary>
private void GetWaitData()
{
SqlConnection DBCon;
SqlCommand Command = new SqlCommand();
SqlDataReader OrdersReader;
IAsyncResult AsyncResult;
System.Threading.WaitHandle WHandle;
DBCon = new SqlConnection();
DBCon.ConnectionString = ConfigurationManager.ConnectionStrings["NorthWindDB"].ConnectionString;
Command.CommandText = @"select top 50 Customers.CompanyName,Customers.ContactName,customers.ContactTitle,
orders.OrderID,Orders.OrderDate,Orders.RequiredDate,orders.ShippedDate
from Orders,Customers
where Orders.CustomerID=customers.CustomerID
order by customers.CompanyName,customers.ContactName";
Command.CommandType = CommandType.Text;
Command.Connection = DBCon;
DBCon.Open();
AsyncResult = Command.BeginExecuteReader();
WHandle = AsyncResult.AsyncWaitHandle;
if (WHandle.WaitOne() == true)
{
OrdersReader = Command.EndExecuteReader(AsyncResult);
gvOrders.DataSource = OrdersReader;
gvOrders.DataBind();
DBCon.Close();
}
else
{
//Asynchronous process has time out.Handle this situation here.
}
}
/// <summary>
/// 使用多个等待句柄,等待全部
/// </summary>
private void GetWaitAllData()
{
SqlConnection DBCon;
SqlCommand OrdersCommand = new SqlCommand();
SqlCommand CustCommand = new SqlCommand();
SqlDataReader OrdersReader;
SqlDataReader CustReader;
IAsyncResult OrdersAsyncResult;
IAsyncResult CustAsyncResult;
System.Threading.WaitHandle[] WHandles = new System.Threading.WaitHandle[2];
System.Threading.WaitHandle OrdersWHandle;
System.Threading.WaitHandle CustWHandle;
DBCon = new SqlConnection();
DBCon.ConnectionString = ConfigurationManager.ConnectionStrings["NorthWindDB"].ConnectionString;
CustCommand.CommandText = "select * from customers where companyName='Alfreds Futterkiste'";
CustCommand.CommandType = CommandType.Text;
CustCommand.Connection = DBCon;
OrdersCommand.CommandText = @"select top 50 Customers.CompanyName,Customers.ContactName,customers.ContactTitle,
orders.OrderID,Orders.OrderDate,Orders.RequiredDate,orders.ShippedDate
from Orders,Customers
where Orders.CustomerID=customers.CustomerID
order by customers.CompanyName,customers.ContactName";
OrdersCommand.CommandType = CommandType.Text;
OrdersCommand.Connection = DBCon;
DBCon.Open();
CustAsyncResult = CustCommand.BeginExecuteReader();
OrdersAsyncResult = OrdersCommand.BeginExecuteReader();
CustWHandle = CustAsyncResult.AsyncWaitHandle;
OrdersWHandle = OrdersAsyncResult.AsyncWaitHandle;
WHandles[0] = CustWHandle;
WHandles[1] = OrdersWHandle;
System.Threading.WaitHandle.WaitAll(WHandles);
CustReader = CustCommand.EndExecuteReader(CustAsyncResult);
OrdersReader = OrdersCommand.EndExecuteReader(OrdersAsyncResult);
gvCustomers.DataSource = CustReader;
gvCustomers.DataBind();
gvOrders.DataSource = OrdersReader;
gvOrders.DataBind();
DBCon.Close();
}
/// <summary>
/// 使用多个等待句柄,等待部分
/// </summary>
private void GetWaitAnyData()
{
SqlConnection DBCon;
SqlCommand OrdersCommand = new SqlCommand();
SqlCommand CustCommand = new SqlCommand();
SqlDataReader OrdersReader;
SqlDataReader CustReader;
IAsyncResult OrdersAsyncResult;
IAsyncResult CustAsyncResult;
int WHindex;
System.Threading.WaitHandle[] WHandles = new System.Threading.WaitHandle[2];
System.Threading.WaitHandle OrdersWHandle;
System.Threading.WaitHandle CustWHandle;
DBCon = new SqlConnection();
DBCon.ConnectionString = ConfigurationManager.ConnectionStrings["NorthWindDB"].ConnectionString;
CustCommand.CommandText = "select * from customers where companyName='Alfreds Futterkiste'";
CustCommand.CommandType = CommandType.Text;
CustCommand.Connection = DBCon;
OrdersCommand.CommandText = @"select top 5 Customers.CompanyName,Customers.ContactName,customers.ContactTitle,
orders.OrderID,Orders.OrderDate,Orders.RequiredDate,orders.ShippedDate
from Orders,Customers
where Orders.CustomerID=customers.CustomerID
order by customers.CompanyName,customers.ContactName";
OrdersCommand.CommandType = CommandType.Text;
OrdersCommand.Connection = DBCon;
DBCon.Open();
CustAsyncResult = CustCommand.BeginExecuteReader();
OrdersAsyncResult = OrdersCommand.BeginExecuteReader();
CustWHandle = CustAsyncResult.AsyncWaitHandle;
OrdersWHandle = OrdersAsyncResult.AsyncWaitHandle;
WHandles[0] = CustWHandle;
WHandles[1] = OrdersWHandle;
for (int Index = 0; Index < 2; Index++)
{
WHindex = System.Threading.WaitHandle.WaitAny(WHandles);
switch (WHindex)
{
case 0:
CustReader = CustCommand.EndExecuteReader(CustAsyncResult);
gvCustomers.DataSource = CustReader;
gvCustomers.DataBind();
break;
case 1:
OrdersReader = OrdersCommand.EndExecuteReader(OrdersAsyncResult);
gvOrders.DataSource = OrdersReader;
gvOrders.DataBind();
break;
default:
break;
}
}
DBCon.Close();
}
}
}